A method of obtaining a real image of an object by making plane waves enter the object and repeatedly carrying out Fourier transform in real space and reciprocal space based on diffracted images from the object is referred to as the “Fourier iterative phase retrieval method” or simply “phase retrieval method” (referred to here as “phase retrieval method”), and it is well-known that spatial resolution of a wavelength order of an incident wave can be obtained in principle (Non-Patent Document 1).
FIG. 1 schematically shows diffraction phenomena. First, source (source of incident waves) 1, sample 3 and detector 5 are arranged as shown in FIG. 1. In this state, waves outputted from source 1 enters sample 3 and scatters, and are recorded by detector 5. At this time, information recorded in detector 5 is generally the intensity of diffracted waves, and amplitude can be obtained from this information, but phase of the diffracted waves cannot be obtained. If phase is obtained, information (images) of the object can be obtained by Fourier transform of the diffracted waves. It is well-known that phase can be obtained by the phase retrieval method by adding certain constraint conditions, and as described above, spatial resolution of a wavelength order of the incident waves can be obtained in principle.
Therefore, when the phase retrieval method is applied to an electron microscope, spatial resolution of an electron de Broglie wavelength decided by an accelerating voltage is expected.
Non-Patent Document 2 reports the success of the observation of nanotubes using a field-emission transmission electron microscopy (Made by JEOL: JE0L2010F), and achievement of spatial resolution of one Angstrom that is less than 2.2 Angstroms guaranteed by the apparatus.
Non-Patent Document 1: R. W. Gerchberg and W. O. Saxton, “A practical algorithm for the determination of phase from image and diffraction plane pictures”, Optik (Stuttgart), vol. 35, pp. 237-246, 1972
Non-Patent Document 2: J. M. Zuo et al., “Atomic Resolution Image of a Carbon Nanotube from Diffraction Intensities”, SCIENCE, vol. 300, pp. 1419-1421, 2003